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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

220                                ALASKAN GLACIER STUDIES
level and in this case it is very clear that the four hundred feet of discordance measures5 the difference in erosive power of the former Russell Fiord Glacier and the smaller ice stream of its tributary, the Hidden Glacier. That the Hidden Glacier was not wanting in erosive power is evidenced by its steep valley walls below sea level in Seal Bay as well as above sea level near the present glacier. The lip of this hanging valley also testifies, by its position well out in the fiord, that the Hidden Glacier pushed the Russell Fiord Glacier well to the west at their junction, thus lessening the discordance of junction. That Hidden Glacier did not erode as fast as the main ice stream, however, is shown conclusively by this submerged hanging valley.
The hanging valley condition also exists near Cape Enchantment, the junction of Nunatak and Russell Fiords, where the distributary of Hubbard-Variegated Glacier moving southeastward in the northwest arm of Russell Fiord was evidently stronger than the former Nunatak Glacier. The amount of discordance may be as great as 444 feet or as little as 200 feet, depending on whether there is a submerged moraine here. It is clear from these soundings near Cape Enchantment, and from the upslope toward Varie-
BAY
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FIG. 18.   CBOSS-SEOTION ov DIHHNCHANIMHNT BAY.   VERTICAL AND HORIZONTAL SCALES THE SAME.
gated Glacier, that the ice from Nunatak Fiord did not move northwestward toward Hubbard Glacier for a very long time.1 That this hanging valley is not due to faulting is shown specifically by two soundings of 888 feet, on either side of a fault line which traverses the fiord bottom. The cliff of the hanging valley is a mile east of this fault.
A third pronounced case of topographic discordance below sea level is the channel east of Haenke Island in Disenchantment Bay, whose relationship to Disenchantment Bay is very much like that of the valleys north and south of the nunatak of Nunatak Glacier. The end of this channel hangs at least two or three hundred feet above the-main Disenchantment Bay, the depths of water in the western part of which are still partly undetermined.
It is to be noted that these submerged discordances (200 to 450 feet) are less than those above sea level, for example 1800 feet in one hanging valley of Nunatak Fiord, and perhaps 1500 or 2000 feet in others. This is because glaciers which are large enough to-descend to sea level usually are less discordant in size and power than those small glaciers-which do not reach the sea.
The soundings also reveal the total amount of discordance of a number of hanging val-
i That one of the last movements was northwestward is amply proved by descending glacial grooves, roche moutonn&s forms with crag and tail details, etc. See Professional Paper 64, U. S. Geol. Survey, 1009, p. 119,